Project Summary/Abstract The success of any bacterial pathogen ultimately depends on its ability to multiply and transmit to new hosts. Mycobacterium tuberculosis (Mtb), the causative agent of the human disease tuberculosis and one of the most successful pathogens in human history, likely also employs sophisticated means to spread from one person to the next, including mediating caseation, tissue destruction, and airborne transmission. Yet, despite the toll Mtb has taken on world health, the molecular mechanisms responsible for Mtb transmission remain elusive. Epidemiologic studies have demonstrated that Mtb strains representing specific lineages are more prevalent in humans. Differences in virulence of specific strains have been proposed to account for the spread of specific strains. However, whether there are differences in transmission and associated factors such as cough induction and aerosolization of bacteria is unknown. These mechanisms may also account for the spread of multidrug-resistant and extensively drug resistant. Thus, there is an urgent need to better characterize the transmission dynamics of Mtb. Historical data is consistent with airborne transmission of Mtb by infected to non-infected guinea pigs. Recently, a mouse model of tuberculosis using the C3HeB/FeJ mouse strain has demonstrated pathologic feature similar to human disease such as caseation and cavitation, suggesting that these animals may also be able to produce Mtb-containing aerosols. Thus, using both guinea pigs and C3HeB/FeJ mice, we will apply bioengineering, microbiology and animal models to characterize Mtb transmission. In the proposed research we will (1) Construct a sophisticated Mtb transmission system to measure transmission, cough and aerosolized particles safely and quantitatively and (2) Use the system to compare the transmissibility of a variety of Mtb species with known differences in worldwide prevalence and innate virulence. The proposed work is expected to identify novel factors associated with transmission, and create a simple, cheap and portable system for future transmission studies that will include comparisons of drug-sensitive to drug-resistant Mtb.